This invention relates to a cathode ray tube screen exposure device and more particularly to means for achieving fine alignment adjustment of related components in the optical system employed in the screen exposure device.
A cathode ray tube of the type utilized in image reproduction, such as in color television, conventionally employs one or more electron guns to provide the electron beam or beams utilized to effect the display. In operation, the modulated electron beams are pre-determinately deflected across the screen of the tube to provide electron impingement upon selected color-emitting phosphor configurations comprising the patterned screen disposed on the tube viewing panel, whereat the transmitted color display is reproduced. It is usual practice to interpose a multi-apertured grid, mask, or other type of negative structure between the electron gun assembly and the screen structure of the tube to provide either masking of the screen, or deflection or focusing of the electron beam or beams thereat.
In the conventional color cathode ray tube, the electron sensitive screen is generally comprised of a repetitive pattern of multitudinous dot, bar, or stripe formations of various phosphors capable of emitting, for example, green, red and blue color luminescence upon electron beam impingement. In some tubes, the pattern of phosphors is disposed to overlay the multitudinous window areas of an opaque screen matrix formed on the viewing portion of the panel. The configurations of the matrix windows and the associated color-phosphor patterns constituting this type of screen construction are formed in accordance with the number of electron guns utilized and with the discrete aperture configurations and operative characteristics of the grid or mask employed in the respective tube.
Since innumerable color phosphor groups are required to produce a high resolution display of desired color purity, the process employed in forming both the windowed matrix and the phosphor screen must be one that is capable of accurately forming a multitude of similar discrete configurations in the screen structure. In a preferred method for fabricating the color screen structure, a photo-printing technique is utilized wherein the tube viewing panel, having an interior coating of photo-sensitive resist composition disposed thereon, is positioned upon an exposure device and suitably photo-exposed through the related negative or multi-apertured mask by radiant energy emanating from a specifically oriented light means within the device. Subsequent development of the selectively exposed panel produces either a first window pattern of the matrix, or in proper sequence, the first color phosphor pattern of the subsequently formed screen. Such photo exposure is sequentially repeated in the proper steps of the procedure to form the remaining windows in the matrix and to later effect deposition of the respective color-emitting phosphor materials associated therewith to complete the fabrication of the patterned screen construction. In separately producing the matrix and the related patterned array of phosphor elements, the light means providing the radiant energy utilized in photo-deposition is appropriately offset from a central axis during the exposure operation for each of the respective color phosphor patterns and definitive window areas constituting the screen.
The screen forming device employed in exposing the sensitized screening material for color cathode ray tubes of the above described type, is conventionally known in the art as a "lighthouse." This structure contains an optical system comprising a light permeable refractive medium or corrective lens and a conjunctive light means relatively positioned to provide the required amount of radiant or actinic energy for proper exposure activation of the light-sensitive coating disposed on the viewing area of the panel. For example, to produce the desired pattern of both the matrix and the phosphor elements of the screen structure, the components of the optical system are oriented or aligned relative to an optical axis in a manner to radiate light over the whole of the multi-apertured mask. Thus, the actinic energy traverses the apertures therein to expose discrete areas, be they matrix windows or the subsequently disposed phosphor dots or stripes, on the respectively sensitized screen material therebehind to thereby produce a patterned array of defined configurations having exactness in accordance with the registration requirements of subsequent electron beam impingement in the finished tube. Several factors determine the optimum setup of the exposure optical system, whereupon the screen-lens-light-means distance relationships are altered depending upon variables such as: the size and shape of the screen, the sensitivity of the photoresist material, and the size and shape of the mask apertures.
It has been found that the relationship of the several components comprising the optical system of the exposure device require precise alignment which is often difficult to achieve because of mechanical tolerances and inherent inaccuracies. The light distribution evidenced from a given alignment setup of the optical components is not always uniform at the screen area of the panel. In attempting to achieve the desired uniformity of exposure radiation across the screen area, a number of time-consuming setup modifications are required. The non-uniformity of light distribution may be due to misalignment of the light output area such as the collector, the light means, or the reflector; and optimum results may necessitate a slight shift of one or more elements from axial alignment per se. The imbalance in light distribution is particularly evidenced in circumferential variations of radiant energy relative to the optical axis, the correction of which often requires a plurality of painstaking adjustments. Consequently, the optimized functioning of the optical system to provide uniform light output, is often not attained in screen exposure, as it is difficult to effect minute adjustments to the system during operation of the device.